1. Field of the Invention
The present invention deals with the field of spherical plain bearings which, by definition, have spherical contact surfaces which allow the inner ring to rotate freely with multiple degrees of freedom while positioned within the bearing outer ring. This multiple movement capability gives this type of bearing the ability to self-align such that it automatically adjusts to any misalignment which may occur due to application requirements or machining tolerances, welding distortions or mounting deformations due to any static and dynamic forces. Machining and distortion misalignment difficulties normally would generate considerable end loading and cause the early failure of conventional plain cylindrical sleeve bearings. Spherical plain bearings have been devised for the purpose of accommodating application, manufacturing and distortion misalignment for which sleeve bearings are not capable or are inadequate.
The main problem with respect to such spherical plain bearings is in the difficulty in positioning of the inner ring with the outer ring during assembly thereof. Since the outer ring has a spherical bearing surface it normally has a side aperture smaller than the size of the inner ring and thereby placement of the inner ring within the bearing cavity of the outer ring becomes a problem.
Originally this problem was overcome by forming of loading slots on diametrically opposite sides of the outer ring which were slightly wider than the inner ring. With such a configuration the bearing can be easily assembled merely by rotating the inner ring ninety degrees and sliding it through this loading slot followed by re-rotating of the inner ring back to the operating position, which will also retain the inner ring within the outer ring.
Such side loading through a mounting slot generated numerous other problems. For example, it usually required the removal of a significant portion of the contact area between the bearing surfaces which appreciably reduces the radial and thrust capacity of the bearing in the direction of the loading slots. Also it made the final bearing assembly more sensitive to the orientation of the loading slots relative to the main load direction.
Also lubrication became a problem since it could easily be lost from the spherical bearing surfaces by escaping through the loading slots in the outer ring. Under some applications the use of such loading slots is possible whenever the problem associated with slotting are not encountered. Normally this bearing is used in situations where fracturing of the outer ring is not utilized because the steel from which the outer ring is made is too soft for fracturing and also it is used in other specific situations which require a non-fractured outer ring for one reason or another.
In most applications the use of the loading slot was ultimately replaced by the fracturing or actual breaking of the outer ring. At some times one would fracture at a single location and at other times at double locations. This fractured ring can then be separated to allow placement of the inner ring within the outer ring and will then be closed when placed at the location of use of the bearing. Normally the environmental structure will retain the fractured bearing outer ring closely thereby presenting no problems due to the fracture therein.
The advantage of this design is that it is not sensitive to the specific orientation of the fracture plane with respect to the load direction as long as the outer ring maintains a press fit inside a sufficiently rigid bore defined in a housing. With such a fractured ring configuration normally the lubrication holes are located at a location away from the point of fracture. Fracturing becomes more difficult with the use of bearings which require additional structural strength since fracturing of the more strong or ductile steel compounds, that is, those with lower carbon content is more difficult. Such low carbon or medium carbon steel materials tend to be more ductile and generally softer and, as such it is generally more difficult to fracture or break during the manufacturing process. On the other hand the high carbon content steel tends to be more brittle and abrasive but has significantly enhanced resistance to frictional wear. Such material can be easily fractured, however it also is easily broken or cracked structurally and therefore the integrity can be compromised. For this reason many bearings are made with an interior core of softer more ductile steel for strength and an exterior skin which is surface hardened or case hardened to prevent wear.
One problem here is that in order to form an outer ring configuration with sufficient structural strength the amount of ductile steel used within the core which is difficult to break is significant thereby greatly restricting the ability to form a bearing by the use of the fracture design. Such bearings are commonly used in heavy load applications such as heavy duty off-road vehicles such as graders and mobile hydraulic cranes, hauling trucks, forklift trucks, front-end loaders, log skidders and various types of fully tracked vehicles.
2. Description of the Prior Art
Numerous processes and configurations have been utilized to increase the hardness of bearings while at the same time maintaining a strong more ductile interior structural core. The use of this process with fractured bearings is currently unknown. Examples of similar bearing configurations for similar purposes and addressing similar applications are shown in U.S. Pat. No. 3,677,032 patented Jul. 18, 1972 to T. Suzuki and assigned to Nippon Seiko Kabushiki Kaisha on a "Shell Type Needle Bearing"; and U.S. Pat. No. 3,737,204 patented Jun. 5, 1973 to E. Burkhardt and assigned to FMC Corporation on an "Extended Life Bearing"; and U.S. Pat. No. 3,795,960 patented Mar. 12, 1974 to J. Elmore et al and assigned to The Torrington Company on a "Method Of Forming Outer Bearing Races"; and U.S. Pat. No. 3,831,241 patented Aug. 27, 1974 to J. Elmore et al and assigned to The Torrington Company on a "Radial And Thrust Bearing And Method Of Making Same"; and U.S. Pat. No. 3,899,225 patented Aug. 12, 1975 to J. Elmore et al and assigned to The Torrington Company on a "Radial And Thrust Bearing"; and U.S. Pat. No. 3,913,988 patented Oct. 21, 1975 to S. Scales et al and assigned to Hughes Tool Company on a "Journal Bearing And Method Utilizing High Carbon Surface"; and U.S. Pat. No. 3,954,517 patented May 4, 1976 to C. Jatczak et al and assigned to The Timken Company on a "Method For Making Carburized Bearing Members"; and U.S. Pat. No. 4,004,952 patented Jan. 25, 1977 to C. Jatczak et al and assigned to The Timken Company on "Carburized Bearing Members"; and U.S. Pat. No. 4,012,238 patented Mar. 15, 1977 to S. Scales and assigned to Hughes Tool Company on a "Method Of Finishing A Steel Article Having A Boronized And Carburized Case"; and U.S. Pat. No. 4,495,006 patented Jan. 22, 1985 to W. Aves, Jr. and assigned to Dresser Industries, Inc. on "Borocarburizing Ferrous Substrates"; and U.S. Pat. No. 4,659,241 patented Apr. 21, 1987 to E. Bamberger et al and assigned to General Electric Company on a "Rolling Element Bearing Member"; and U.S. Pat. No. 4,664,722 patented May 12, 1987 to D. Clinkscales et al and assigned to Hughes Tool Company-USA on a "Method For Protecting From Hardening A Selected Region Of A Steel Structure"; and U.S. Pat. No. 4,871,268 patented Oct. 3, 1989 to K. Furumura et al and assigned to Nippon Seiko Kabushiki Kaisha on a "Rolling Bearing"; and U.S. Pat. No. 4,888,065 patented Dec. 19, 1989 to K. Grell and assigned to INA Walzlager Schaeffler KG on a "Method Of Making Roller Bearing Element And Product Therefrom"; and U.S. Pat. No. 4,904,094 patented Feb. 27, 1990 to K. Furumura et al and assigned to Nippon Seiko Kabushiki Kaisha on a "Ball-And-Roller Bearing System"; and U.S. Pat. No. 4,913,749 patented Apr. 3, 1990 to F. Hengerer et al and assigned to SKF GmbH on a "Process For Case-Hardening Rolling Bearing Elements Of Low-Alloy Nickeliferous Steel"; and U.S. Pat. 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Toda and assigned to Koyo Seiko Co., Ltd. on "Bearing Components And Process For Producing Same"; U.S. Pat. No. 5,413,643 patented May 9, 1995 to Y. Murakami et al and assigned to NSK Ltd. on a "Rolling Bearing"; and U.S. Pat. No. 5,531,836 patented Jul. 2, 1996 to M. Dezzani et al and assigned to The Torrington Company on a "Rolling Bearing And Method Of Making Same"; and U.S. Pat. No. 5,560,787 patented Oct. 1, 1996 to M. Takagi et al and assigned to NSK Ltd. on a "Rolling Bearing For High-Speed Rotation At High Temperatures"; and U.S. Pat. No. 5,567,508 patented Oct. 22, 1996 to Y. Murakami and assigned to NSK Ltd. on a "Rolling Bearing With Surface Hardened Layer"; and U.S. Pat. No. 5,648,611 patented Jul. 15, 1997 to S. Singh et al and assigned to The Timken Company on a "Process For Measuring The Case Depth Of Case-Carburized Steel"; and U.S. Pat. No. 5,698,159 patented Dec. 16, 1997 to T. Ochi et al and assigned to Nippon Steel Corporation on a "Long-Life Carburizing Bearing Steel"; and U.S. Pat. No. 5,780,165 patented Jul. 14, 1998 to S. Fukumoto et al and assigned to Hitachi Metals, Ltd. on a "Bearing Steel Bearing Member Having Excellent Thermal Resistance And Toughness".